This invention relates to fuel supply systems in internal combustion engines, and more particularly to improvements in a fuel supply system for an internal combustion engine, suitable for use in an engine of a motor vehicle provided with an electronic fuel injection device, and comprising injectors for injecting fuel, a fuel flow path for supplying fuel to the injectors and an assist air flow path for supplying assist air to expedite the spraying of fuel to the neighborhood of jets of the injectors.
2. Description of the Prior Art
Systems for controlling an air-fuel ratio of a gas mixture in an internal combustion engine of a motor vehicle and the like include one wherein an electronic fuel injection device is used. In this internal combustion engine provided with the electronic fuel injection device, a fuel injection time is determined in accordance with an intake air flow rate of the engine and an engine rotational speed for example, and injectors provided on an intake manifold for example, for injecting fuel towards an intake port of the engine are opened, whereby the air-fuel ratio of the engine is controlled, and hence, these electronic fuel injection devices have been widely used in the engines for motor vehicles, wherein the air-fuel ratio must be precisely controlled and an exhaust emission control measure is taken. In the internal combustion engines provided with the electronic fuel injection device of the type described, in general, there is provided a fuel delivery pipe passing through the neighborhood of the rear portion of the respective injectors, and fuel is adapted to be supplied to the respective injectors through the fuel delivery pipe. However, when a continuous high load driving is effected under high temperature for example, fuel is evaporated in the fuel delivery pipe, and a sufficient supply of fuel is not injected from the injectors due to a vapor lock, whereby the air-fuel ratio tends to become lean. To obviate the above-described disadvantage, heretofore, the fuel delivery pipe has been spaced apart from a heat source such as an exhaust manifold, which, however, could not obtain a satisfactory result.
On the other hand, recently, such an attempt has been made that part of intake air is fed to the neighborhood of the jets of the injectors to improve the spraying of the fuel to be injected from the injectors by the flow velocity of air, thus enabling to obtain a certain result. However, heretofore, the assist air piping has been disposed independently of the aforesaid fuel delivery pipe and the like, being not utilized for cooling the fuel or the like.
In addition, it is conceivable to provide a separate fuel cooling device, which, however, may result in complicated construction and increased costs.